Abstract
Few layer black phosphorus (BP) with unique in-plane puckered crystalline structure has attracted intense interest for strain engineering owing to both its significant anisotropy in mechanical and electrical properties as well its remarkably high intrinsic strain limit. Here we investigated the phonon response of few layer BP under uniaxial tensile strain (~7%) with in-situ polarized Raman spectroscopy. Together with the first-principle density functional theory (DFT) analysis, the anisotropic Poisson’s ratio in few layer BP was verified as the primary factor that caused the large discrepancy in both the slope and trend in reported Raman frequency shift for strained BP, armchair (AC) direction in particular. By carefully include and exclude the anisotropic Poisson’s effect in the DFT emulations, we rebuilt both trends reported for Raman modes shift. Furthermore, the angle-resolved Raman spectroscopy was conducted in-situ under tensile strain for systematic investigation of the in-plane anisotropy of BP phonon response. The experimentally observed thickness and crystallographic orientation dependence is elaborated using DFT theory as strong correlation between the strain perturbated electronic band structure and the phonon vibration modes. This study has provided bright insight, both experimentally and theoretically, for the complex electron-phonon interaction behavior in strained BP, which enables diverse possibilities for strain engineering of electrical and optical properties in BP and alike two-dimensional (2D) nano materials.
